Among thirteen isolated meningococcal serogroups, A, B, C, W-135, and Y are the most prevalent. There are three FDA-approved capsular polysaccharide (PS)-based vaccines—Menomune® tetravalent PS vaccine (Sanofi Pasteur), and Menactra® (Sanofi Pasteur) and Menveo® (Novartis) tetravalent conjugate vaccines for protection against meningococcal disease caused by groups A, C, W-135, and Y Neisseria meningitidis. Group B capsular PS, a polysialic acid with an α2→8 glycosidic linkage, is similar to the PS structure expressed in certain human tissues (Finne et al., Lancet 2:355-357, 1983), thus making it a poor immunogen. Furthermore, if used as a vaccine, the possibility exists of it inducing an autoimmune response. Thus, a need remains to develop additional meningococcal vaccines, particularly for group B and group X meningococcal serogroups.